Method for producing single crystal sic substrate and single crystal sic substrate produced by the same

ABSTRACT

A single crystal SiC substrate is produced with low cost in which a polycrystalline SiC substrate with relatively low cost is used as a base material substrate where the single crystal SiC substrate has less strain, good crystallinity and large size. The method including a P-type ion introduction step of for implanting P-type ions from a side of a surface Si layer  3  into an SOI substrate  1  in which the surface Si layer  3  and an embedded oxide layer  4  having a predetermined thickness are formed on an Si base material layer  2  to convert the embedded oxide layer  4  into a PSG layer  6  to lower a softening point, and an SiC forming step for heating the SOI substrate  1  having the PSG layer  6  formed therein in an atmosphere hydrocarbon-based gas to convert the surface Si layer  3  into SiC, and thereafter, cooling the resulting substrate to form a single crystal SiC layer  5  on a surface thereof.

TECHNICAL FIELD

The present invention relates to a method for producing a single crystalSiC substrate and the single crystal SiC substrate; specifically relatesto a method for producing a single crystal SiC substrate in which asingle crystal SiC substrate having a large size, good crystallinity andless strain can be produced, and the single crystal SiC substrate.

RELATED ART

Single crystal SiC (silicon carbide) is excellent in thermal andchemical stability, high in mechanical strength and resistant toirradiation, and due to these properties, has attracted an attention asa semiconductor device material for the next generation. Particularly,the single crystal SiC is considered to be promising in a technicalfield of substrate material such as a blue light emitting diode, anenvironmentally-resistant semiconductor device and the like. As a methodfor obtaining an SiC film used for such an application, there aregenerally used a liquid phase growth method at a temperature of 1400° C.or more, or a gas-phase growth method at a temperature of 1300° C. ormore on a substrate of SiC single crystal.

However, in the above method in which the SiC single crystal is used asstarting material, the obtainable SiC single crystal itself is highlyexpensive and has a small area in fact. Therefore, it is extremelyexpensive as a semiconductor device as well, thus, strongly demanded isa technique to provide a single crystal SiC substrate having a largearea at low cost.

Therefore, as disclosed in Patent Document 1 below, a technique has beenprovided in which utilizing an insulation-layer-embedded type Sisubstrate having a surface Si layer as well as an embedded insulationlayer (SiO₂ layer) and an Si base material layer under the surface Silayer, the surface Si layer of the insulation-layer-embedded type Sisubstrate is formed into a thin film of around 10 nm, which is subjectedto a carbonization process at a high temperature to convert it into asingle crystal SiC layer.

Patent Document 1: JP 2003-224248(A)

Patent Document 2: JP 2001-094082(A)

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

However, in the producing method described above, Si, having a meltingpoint of 1410° C., cannot be subjected at all to the high temperatureprocess at 1400° C. or more, and needs to be subjected to thecarbonization process at a temperature at least lower than 1400° C. Onthe other hand, since coefficients of thermal expansion are differentbetween Si and SiC, and a softening point of SiO₂ is relatively higharound 1200° C., there have been problems in which a difference ofshrinkage ratios occurring between the Si base material layer and theSiC layer in the step of cooling after heating in the carbonizationprocess and the substrate after cooling cannot be prevented fromwarping. The warp is generated in the substrate itself in this way, thusin fact; there has been a limitation on growing in size of thesubstrate. Thus, in the current technique, the single crystal SiCsubstrate only with high film quality is expensive and of small size isobtained, and a single crystal SiC substrate of a large size and highfilm quality cannot be obtained in fact. Therefore, a technique toprovide the single crystal SiC substrate having a large size and goodcrystallinity at low cost has been strongly demanded to be developed.

The present invention is made in consideration of the above-describedproblem, and has an object to provide a method for producing a singlecrystal SiC substrate in which a polycrystalline SiC substrate withrelatively low cost is used as a base material substrate to produce asingle crystal SiC substrate having less strain, good crystallinity andlarge size with low cost, and to provide the single crystal SiCsubstrate as well.

Means for Solving the Problem

In order to achieve the above object, a method for producing a singlecrystal SiC substrate according to an aspect of the invention includes aphosphorous ion introduction step for introducing phosphorous ions froma side of a surface Si layer into an SOI substrate in which the surfaceSi layer and an embedded oxide layer having a predetermined thicknessare formed on an Si base material layer to convert the embedded oxidelayer into an embedded glass layer to lower a softening point, and anSiC forming step for heating the SOI substrate having the embedded glasslayer formed therein in an atmosphere of hydrocarbon-based gas toconvert the surface Si layer into SiC, and thereafter, cooling theresulting substrate to form a single crystal SiC layer on a surfacethereof.

According to another aspect of the invention, a method for producing asingle crystal SiC substrate includes a glass layer forming step for,before joining an Si base material and an Si thin plate constituting asurface Si layer, forming on a surface to be a joint surface thereof, ofat least one of the Si base material and the surface Si layer, a glasslayer having a softening point lower than at least the SiO₂ by adeposition method, a joining step for joining the Si base material andthe Si thin plate so as to sandwich the glass layer therebetween to forman embedded type substrate in which the Si base material layer, thesurface Si layer and the embedded glass layer are laminated, and an SiCforming step for heating the embedded type substrate in an atmosphere ofhydrocarbon-based gas to convert the surface Si layer into SiC, andthereafter, cooling the resulting substrate to form a single crystal SiClayer on a surface thereof.

Further, in order to achieve the above object, a single crystal SiCsubstrate according to an aspect of the invention includes an Si basematerial layer, a single crystal SiC layer which is a surface of the Sibase material layer, and an embedded glass layer having a softeningpoint lower than at least SiO₂ formed between the Si base material layerand the single crystal SiC layer.

Effect of the Invention

That is, the method for producing the single crystal SiC substrateaccording to a first aspect of the invention includes the carbonizationprocess in which an embedded oxide layer in an SOI substrate isconverted into an embedded glass layer having a lower softening point,and thereafter, the resulting substrate is heated in an atmosphere ofhydrocarbon-based gas and cooled. Therefore, even if a difference ofshrinkage ratios is generated between the SiC layer and the Si basematerial layer formed in the carbonization process, the embedded glasslayer between the SiC layer and the Si base material layer istransformed to generate a slip between the Si base material layer andthe SiC layer, greatly suppressing the warp of the entire substrate.

In the method for producing a single crystal SiC substrate according tothe first aspect of the invention, if an introduction amount of thephosphorous ions in the phosphorous ion introduction step is from 1×10¹⁵to 5×10¹⁸ ions/cm², a warp of the substrate can be effectivelysuppressed with crystallinity of the SiC layer formed being maintainedwell.

In the method for producing a single crystal SiC substrate according tothe first aspect of the invention, the substrate temperature is 200 to550° C. in the phosphorous ion introduction step, the crystallinity ofthe surface Si layer is maintained well and a good SiC layer can beensured in the carbonization step.

In the method for producing a single crystal SiC substrate according tothe first aspect of the invention, the phosphorous ion introduction stepis performed by ion implantation, and if an accelerating energy of thephosophrous ions at which the time is 5 to 30 keV, the ion implantationcan be conducted with the crystallinity of the surface Si layer beingmaintained. As a result, warp of the substrate can be effectivelysuppressed.

Further, a method for producing a single crystal SiC substrate accordingto a second aspect of the invention includes a carbonization process inwhich the embedded type substrate is formed which has the embedded glasslayer lower in the softening point than at least the SiO₂ embeddedbetween the Si base material layer and the surface Si layer, andthereafter, the resulting substrate is heated in an atmosphere ofhydrocarbon-based gas and cooled. Therefore, even if a difference ofshrinkage ratios is generated between the SiC layer and the Si basematerial layer formed in the carbonization process, the embedded glasslayer between the SiC layer and the Si base material layer istransformed to generate a slip between the Si base material layer andthe SiC layer, greatly suppressing the warp of the entire substrate.

Moreover, a single crystal SiC substrate according to the inventionincludes the embedded glass layer lower in the softening point than atleast the SiO₂ embedded between the Si base material layer and thesurface single crystal Si layer. Therefore, even if the carbonizationprocess is performed in which the resulting substrate is heated in anatmosphere of hydrocarbon-based gas and cooled, the embedded glass layerbetween the SiC layer and the Si base material layer is transformed togenerate a slip between the Si base material layer and the SiC layer,greatly suppressing the warp of the entire substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A) to 1(C) are views showing a method for producing a singlecrystal SiC substrate according to a first embodiment of the invention.

FIGS. 2(D) to 2(F) are views showing the method for producing the singlecrystal SiC substrate according to the first embodiment of theinvention.

FIG. 3 is a view showing the method for producing the single crystal SiCsubstrate.

FIGS. 4(A) to 4(D) are views showing a method for producing a singlecrystal SiC substrate according to a second embodiment of the invention.

DESCRIPTION OF REFERENCE NUMERALS

1 SOI substrate

2 Si base material layer

3 Surface Si layer

4 Embedded oxide layer, oxide layer

5 Single crystal SiC layer

6 PSG layer

8 GaN layer

BEST MODE FOR CARRYING OUT THE INVENTION

Next, descriptions will be given of the best mode for carrying out theinvention.

First Embodiment

FIGS. 1(A) to 1(C) and FIGS. 2(D) to 2(F) are views showing a method forproducing a single crystal SiC substrate according to a first embodimentof the invention.

The method for producing the single crystal SiC substrate performs Steps(1) and (2) below.

(1) A phosphorous ion introduction step in which phosphorous ions areintroduced from a side of a surface Si layer 3 to an SOI (Silicon OnInsulator) substrate 1 in which a surface Si layer 3 and an embeddedoxide layer 4 having a predetermined thickness are formed on an Si basematerial layer 2 to convert the embedded oxide layer 4 into a PSG layer6 as an embedded glass layer and lower a softening point.

(2) A SiC forming step in which the SOI substrate 1 having the PSG layer6 as the above-mentioned embedded glass layer formed therein is heatedin an atmosphere of hydrocarbon-based gas to convert the surface Silayer 3 into SiC, and thereafter, is cooled to form a single crystal SiClayer 5 on a surface thereof.

FIG. 1(A) shows the SOI substrate 1 in which the surface Si layer 3 andthe embedded oxide layer 4 having a predetermined thickness on a surfaceof the Si base material layer 2. The SOI substrate 1 is configured sothat the SiO₂ layer having the predetermined thickness as the embeddedoxide layer 4 is formed near the surface of the Si base material layer2, and on a surface thereof formed is the surface Si layer 3 having thepredetermined thickness. The thickness of the embedded oxide layer 4 isset to be about 100 to 200 nm. The surface Si layer 3 of the SOIsubstrate 1 having a thickness of about 20 nm to 50 nm is made thinnerto about 4 nm to 10 nm for use. The thinning process is performed in amanner in which, for example, the SOI substrate 1 is subjected to a heattreatment in an oxidation atmosphere to be oxidized from the surface ofthe surface Si layer 3 by a predetermined depth for the Si layer havinga desired thickness to be remained near an interface with the embeddedoxide layer 4, and then, an oxide layer generated on the surface thereofis etched by a hydrofluoric acid or the like to be removed, thinning thesurface Si layer 3.

At this time, the thickness, of the thinned surface Si layer 3 ispreferably set to be about 4 nm to 10 nm as described above, and morepreferably about 4 nm to 7 nm. This is because if the thickness of thethinned surface Si layer 3 is too thin, the single crystal SiC layer 5will not be generated sufficiently in the subsequent converting step asthe carbonization process, and a good single crystal SiC layer 7 cannotbe formed.

On the other hand, if the thickness of the thinned surface Si layer 3 istoo thick, it is difficult to be completely carbonized when beingconverted into the single crystal SiC layer 5 in the subsequentcarbonization process, and a non-carbonized Si layer will be remained onthe bottom end portion of the SiC layer 5. The remained Si layer willeasily disperse to an upper portion of the SiC layer by the subsequentheat treatment, resulting to deteriorate the crystallinity thereof. Thesingle crystal SiC layer 5 may be further epitaxial grown as needed;however, if the crystallinity of the single crystal SiC layer 5 as aseed layer is poor; only the single crystal SiC layer 5 with the poorcrystallinity is obtained even if the epitaxial growth is performed. Inthis way, it is very important to perform the complete carbonization soas not to generate the remained SiC layer.

FIG. 1(B) and FIG. 1(C) show the phosphorous ion introduction step inwhich the phosphorous ions are introduced from the side of the surfaceSi layer 3 of the SOI substrate 1 to convert the SiO₂ constituting theembedded oxide layer 4 into a phosphor-silicate glass (PSG) in whichphosphorus is introduced, to form the PSG layer 6 and lower thesoftening point.

The phosphorous ion introduction step can be performed by, for example,ion implantation and a plasma doping method or the like.

An introduction amount of the phosphorous ions in the phosphorous ionintroduction step, that is, a dose amount is preferably 1×10¹⁵ to 5×10¹⁸ions/cm². This is because an extent of softening of the PSG layer 6 isnot sufficient with the dose amount less than 1×10¹⁵ ions/cm², and thus,an effect for preventing warp of the substrate cannot be obtainedsufficiently. In contrast, if the dose amount exceeds 5×10 ¹⁸ ions/cm²,the crystallinity of the surface Si layer 3 is lowered, not obtainingthe single crystal SiC layer 5 of good quality and good crystallinity.In this way, the dose amount in the phosphorous ion introduction step isset to 1×10¹⁵ to 5×10¹⁸ ions/cm² to allow to effectively suppress thewarp of the substrate while the crystallinity of the single crystal SiClayer 5 to be formed is successfully maintained.

The doping amount of phosphorus for the PSG layer 6 by the ionimplantation is preferably set to about 5 to 7 atom %. This is becauseif the doping amount is less than 5 atom %, the extent of softening ofthe PSG layer 6 is not sufficient, and an effect for preventing warp ofthe substrate cannot be obtained sufficiently. In contrast, the dopingamount exceeds 7 atom %, hygroscopicity of the PSG layer 6 is raised,and electrical characteristics of an electron device formed using thesingle crystal SiC layer 5 is seriously deteriorated, not obtaining theelectron device of good quality and high reliability. In this way, thedoping amount of phosphorus to the glass constituting the PSG layer 6 isset to 5 to 7 atom % to allow to effectively suppress the warp of thesubstrate while the electrical characteristics of the single crystal SiClayer 5 is successfully maintained.

Moreover, the substrate temperature in the phosphorous ion introductionstep is preferably set to 200 to 550° C. If the substrate temperature isless than 200° C., the crystallinity of the surface Si layer 3 islowered, and the single crystal SiC layer 5 of good quality and goodcrystallinity cannot be obtained. In contrast, if the substratetemperature exceeds 550° C., Si constituting the surface Si layer 3begins to sublimate to reduce the thickness, therefore, not obtainingthe single crystal SiC layer 5 having enough thickness. In this way, thesubstrate temperature in the phosphorous ion introduction step is set to200 to 550° C. to allow successfully maintaining the crystallinity ofthe single crystal SiC layer 5 and ensure suitable thickness.

If the phosphorous ion introduction step is performed by ionimplantation, an accelerating energy of the phosphorous ions at thattime is preferably set to 5 to 30 keV. This is because if theaccelerating energy is either less than 5 keV or more than 30 keV, theembedded oxide layer 4 cannot be converted into the PSG layer 6 havingan enough lower softening point in terms of thickness of the surface Silayer 3. Therefore, the accelerating energy is set to 5 to 30 keV toallow to effectively suppress the warp of the substrate whilemaintaining the crystallinity of the SiC layer and suitable thickness.

FIG. 2(D) shows a state where the SiC forming step is performed in whichthe SOI substrate 1 having the PSG layer 6 as the embedded glass layerformed therein is heated in an atmosphere of hydrocarbon-based gas toconvert the surface Si layer 3 into SiC and then is cooled to form thesingle crystal SiC layer 5 on the surface thereof.

The SiC forming step can be performed by, for example, changing over theatmosphere gas (hydrogen gas and hydrocarbon gas) introduced in thefurnace which can control the atmosphere to adjust the temperature.

With an apparatus as mentioned above, the SOI substrate 1 is placed inthe furnace, and a mixture gas of hydrogen gas and hydrocarbon-based gasis supplied into the furnace to raise the temperature of the atmospherein the furnace to convert the surface Si layer 3 of the SOI substrate 1into the single crystal SiC layer 5.

At this time, the SOI substrate 1 is placed in the furnace, and themixture gas in which the hydrocarbon-based gas is mixed to the hydrogengas at a ratio of 1 vol. % is supplied into the furnace. Further, at thesame time as the supply of the mixture gas, the atmosphere temperaturein the furnace is heated to 900 to 1405° C. With the heating, thesurface Si layer 3 of the SOI substrate 1 can be converted into thesingle crystal SiC layer 5.

Here, the hydrogen gas is a carrier gas, and as the hydrocarbon gas apropane gas is used, for example. For example, if the supply amount froma canister of hydrogen gas is 1000 cc/min, the supply amount from acanister of hydrocarbon gas is 10 cc/min.

Then, the substrate is heated for a predetermined time, and cooled to aroom temperature after the surface Si layer 3 is completely carbonizedto be converted into the single crystal SiC layer 5. At this time, thePSG layer 6 having a softening point lower than SiO₂ exists between thesingle crystal SiC layer 5 and the Si base material layer 2, therefore,even if a difference of shrinkage ratios is generated between the singlecrystal SiC layer 5 and the Si base material layer 2, which are formedin the carbonization process, the PSG layer 6 between the single crystalSiC layer 5 and the Si base material layer 2 is deformed to generate aslip between the Si base material layer 2 and the single crystal SiClayer 5, enabling to greatly suppress the warp of the entire substrate.

FIG. 2(E) shows a state where the single crystal SiC layer 5 formed asdescribed above is used as the seed layer, and the single crystal SiClayer 5 is further grown epitaxially.

The epitaxial growth is performed, for example, with the followingconditions to epitaxially grow the single crystal SiC layer 5. Forexample, a substrate having the single crystal SiC layer 5 on thesurface thereof is placed inside a processing chamber, and treated at atemperature of 900 to 1405° C. while a material gas ofmethylsilane-based gas such as monomethylsilane is supplied into theprocessing chamber at a gas flow rate of about 1.0 sccm. Thus, byepitaxially growing using the single crystal SiC layer 5 as a seedlayer, the single crystal SiC layer 5 can be grown.

In this way, in heating and cooling in epitaxially growing the singlecrystal SiC layer 5, the PSG layer 6 with a low softening point existsbetween the single crystal SiC layer 5 and the Si base material layer 2;therefore, the PSG layer 6 between the single crystal SiC layer 5 andthe Si base material layer 2 is deformed to generate a slip between theSi base material layer 2 and the single crystal SiC layer 5, enabling togreatly suppress the warp of the entire substrate.

The processing temperature above (the process can be performed withinthe above temperature range) is preferably set to about 1000 to 1350° C.in order to obtain a film with better quality and in view of facilitycost, energy cost, maintenance cost and the like.

Alternatively, the epitaxial growth can be performed by simultaneouslysupplying silane-based gas such as monosilane gas and hydrocarbon-basedgas such as propane gas into the processing chamber to process in theabove temperature range, thus, the single crystal SiC layer 5epitaxially grows.

In this way, the single crystal SiC substrate according to the inventioncan be obtained in which the PSG layer 6 as the embedded glass layerhaving the softening point lower than at least SiO₂ is formed betweenthe Si base material layer 2 and the surface single crystal SiC layer 5.

FIG. 2(F) shows a state where another semiconductor film such as a GaNlayer 8 is formed by the epitaxial growth on the single crystal SiClayer 5 as needed.

The epitaxial growth is performed with, for example, the conditionsbelow to grow the GaN layer 8. For example, a substrate having thesingle crystal SiC layer 5 formed therein is placed in the processingchamber, and is processed at a temperature of 950 to 1200° C., whiletriethylgallium at a flow rate of about 2 sccm and ammonia at a flowrate of about 1250 sccm are supplied into the processing chamber; thus,the GaN layer 8 can be formed on the single crystal SiC layer 5.

In this way, in heating and cooling in epitaxially growing the GaN layer8 on the single crystal SiC layer 5, the PSG layer 6 with a lowsoftening point exists between the single crystal SiC layer 5 and the Sibase material layer 2; therefore, the PSG layer 6 between the singlecrystal SiC layer 5 and the Si base material layer 2 is deformed togenerate a slip between the Si base material layer 2 and the singlecrystal SiC layer 5, enabling to greatly suppress the warp of the entiresubstrate.

FIG. 3 shows results of measuring an amount of warp of the substrates ofan example of the invention and a comparative example.

The SOI substrate 1 was prepared where the surface Si layer 3 having athickness of 7 nm, the Si base material layer 2 having a thickness of725 μm, the embedded oxide layer 4 having a thickness of 160 nm, and adiameter of the substrate is 200 mm.

In the example, the phosphorous ions were implanted to the SOI substrate1 to convert the embedded oxide layer 4 into the PSG layer 6, and then,the carbonization process was preformed. The accelerating energy of theions was set to 30 keV, the dose amount was set to 6×10¹⁵ ions/cm², andthe substrate temperature was set to 250° C. In the comparative examplethe carbonization process was performed without performing implanting ofthe SOI substrate 1 with the ions.

The carbonization process was performed while the mixture gas was flowedat a ratio of the propane gas of 30 cc and the hydrogen gas of 2000 cc,and the substrate was heated at 1250° C. for 15 minutes.

In the subsequent epitaxial growth, the process was performed at atemperature of 1200° C. while the monomethylsilane gas was supplied at agas flow rate of about 3 sccm, and the processing period of time wasvaried to prepare samples having a final thicknesses of the singlecrystal SiC layers 5 at 5 nm, 160 nm, 320 nm, and 600 nm.

The warp amount was measured as follows. That is, a sample to bemeasured having a diameter of 200 mm was placed on a sample measuringpedestal having a horizontal reference plane, and scanned in ahorizontal plane with the surface of the aforementioned sample to bemeasured being contact with a probe of a warp amount probe measurement.At this time, a waviness which appeared in the horizontal plane inresponse to a waviness on the surface of the sample to be measured wasrecorded, and the waviness is measured by determining as the warp amountof the entire substrate.

As seen from FIG. 3, when the thickness of the single crystal SiC layer5 exceeds 300 nm, the example obtained good results. Note that thecomparative example seems to be better with regards to the portionhaving a thinner thickness, however this difference is within the scopeof measurement error, and the suppressing effect of warp notably appearsfrom around a portion where the thickness exceeds 300 nm.

Note that in the above example, a case is shown where only thephosphorous ions were introduced in the ion implantation to convert theembedded oxide layer 4 into the PSG layer 6; however, B-type ions mayadditionally be introduced with the phosphorous ions to convert theembedded oxide layer 4 into the BPSG layer.

Second Embodiment

FIGS. 4(A) to 4(D) are diagrams showing a method for producing a singlecrystal SiC substrate according to a second embodiment of the invention.

The method for producing the single crystal SiC substrate performs Steps(1), (2) and (3) below.

(1) A glass layer forming step of, before joining an Si base materialand an Si thin plate constituting a surface Si layer, forming on asurface, to be a joint surface thereof, of at least one of the Si basematerial and the surface Si layer by a deposition method a glass layerhaving a softening point lower than at least the SiO₂.

(2) A joining step of joining the Si base material and the Si thin plateso as to sandwich the glass layer therebetween to form an embedded typesubstrate in which the Si base material layer, the surface Si layer andthe embedded glass layer are laminated.

(3) An SiC forming step of heating the embedded type substrate in anatmosphere of hydrocarbon-based gas to convert the surface Si layer intoSiC, and thereafter, cooling the resulting substrate to form a singlecrystal SiC layer on a surface thereof.

As shown in FIG. 4(A), in this example, firstly, over the surface of theSi thin plate constituting the surface Si layer 3, a PSG layer 6 isformed by a deposition method, which is a glass layer having a softeningpoint lower than at least the SiO₂.

The deposition method may be applied with various deposition methods,for example, a chemical gas-phase deposition method such as adecompression CVD and a plasma CVD, and a physical gas-phase depositionmethod such as a vacuum deposition method, a sputtering method and thelike.

As shown in FIG. 4(B), the surface Si layer 3 having formed the PSGlayer 6 thereon and the Si base material layer 2 are joined to eachother so as to interpose the PSG layer 6 therebetween. The PSG layer 6is a glass doped with phosphorus, and the doping amount of phosphorus ispreferably set to about 5 to 7 atom %. This is because if the dopingamount is less than 5 atom %, the extent of softening of the PSG layer 6is not sufficient, and thus, an effect for preventing a warp of thesubstrate cannot be obtained enough. In contrast, if the doping amountexceeds 7 atom %, hygroscopicity of the PSG layer 6 is raised, andelectrical characteristics of an electron device formed using the singlecrystal SiC layer 5 is seriously deteriorated, not obtaining theelectron device of good quality and high reliability. In this way, thedoping amount of phosphorus to the glass constituting the PSG layer 6 isset to 5 to 7 atom % to allow to effectively suppress the warp of thesubstrate while the electrical characteristics of the single crystal SiClayer 5 formed is successfully maintained.

The joining can be performed by laminating the surface Si layer 3 andthe PSG layer 6 on an upper surface of the Si base material layer 2 sothat the surface Si layer 3 is oriented upwardly and the PSG layer 6 isoriented downwardly, and heating the resulting substrate. The heatingtemperature at this time is about 850 to 950° C., and the heating timeis about 30 to 60 minutes.

FIG. 4(C) shows the embedded type substrate in which the embedded typePSG layer 6 is laminated between the Si base material layer 2 and thesurface Si layer 3 both formed as the above. In the embedded typesubstrate, the thickness of the PSG layer 6 is set to about 100 to 200nm, and the surface Si layer 3 is thinned to a thickness of 4 nm to 10nm in advance, similar to the first embodiment described above.

Next, the embedded type substrate is heated in an atmosphere ofhydrocarbon-based gas to convert the surface Si layer 3 into SiC, andthen cooled to form the single crystal SiC layer 5 on the surface. Theconditions of the carbonization process are similar to those of thefirst embodiment described above.

FIG. 4(D) shows the embedded type substrate in which the embedded typePSG layer 6 is laminated between the Si base material layer 2 and thesurface Si layer 3 both formed as the above.

Thereafter, the single crystal SiC layer 5 is grown epitaxially andanother semiconductor layer such as the GaN layer 8 is laminated. Theconditions of the epitaxial growth are the same as those of the firstembodiment described above.

In this way, the single crystal SiC substrate according to the inventioncan be obtained in which the PSG layer 6 as an embedded glass layerhaving a softening point lower than at least SiO₂ is formed between theSi base material layer 2 and the surface single crystal SiC layer 5.

Note that, in this example, the PSG layer 6 is formed over the surfaceof the Si thin plate constituting the surface Si layer 3, and then isjoined to the Si base material layer 2. However, the PSG layer 6 isformed over the surface of the Si base material layer 2 and then the Sithin plate constituting the surface Si layer 3 may be joined, or the PSGlayer 6 may be formed over the surfaces of both the Si base materiallayer 2 and the Si thin plate constituting the surface Si layer 3, andthen, both layers may be joined.

In the method for producing the single crystal SiC substrate accordingto this embodiment, the embedded type substrate in which the PSG layer 6having the softening point lower than at least SiO₂ is formed betweenthe Si base material layer 2 and the surface Si layer 3 is formed, andthereafter, the carbonization process of heating the substrate in theatmosphere of hydrocarbon-based gas and cooling the substrate isperformed. Therefore, even if a difference of shrinkage ratios isgenerated between the single crystal SiC layer 5 and the Si basematerial layer 2 formed in the carbonization process, the PSG layer 6between the single crystal SiC layer 5 and the Si base material layer 2is deformed to generate a slip between the Si base material layer 2 andthe SiC layer 5, greatly suppressing the warp of the entire substrate.

Note that the embodiment described above shows a case where the PSGlayer 6 is formed by the deposition method; however, a BPSG layer (boronphosphorus silicon glass layer) may be formed similarly by thedeposition method.

INDUSTRIAL APPLICABILITY

The invention can be applied to production and the like of asemiconductor substrate to be used for a large-scale integrated circuitand the like.

1.-7. (canceled)
 8. A method for producing a GaN substrate, comprising:a phosphorus ion introduction step for introducing phosphorus ions froma side of a surface Si Layer into an SiC substrate in which the surfaceSi layer and an embedded oxide layer having a predetermined thicknessare formed on an Si base material layer to convert the embedded oxidelayer into an embedded glass layer to lower a softening point; and anSiC forming step for heating the SOI substrate having the embedded glasslayer formed therein in an atmosphere of hydrocarbon-based gas toconvert the surface Si layer into SiC, and thereafter, cooling theresulting substrate to form a single crystal SiC layer on a surfacethereof, wherein the SiC forming step further comprises causing theembedded glass layer between the SiC layer and the Si base materiallayer to be transformed to cause slippage between the Si base materiallayer and the SiC layer, to accommodate a difference in shrinkage ratiosbetween the SiC layer and the Si base material layer during performanceof the method, heating and cooling to epitaxially grow the GaN layer onthe single crystal SiC layer, and thereby causing the embedded glasslayer between the SiC layer and the Si base material layer to betransformed to cause slippage between the Si base material layer and theSiC layer, to suppress warp of the entire substrate crystal SiCsubstrate.
 9. The method for producing the GaN substrate according toclaim 8, wherein an introduction amount of the phosphorus ions in thephosphorus ion introduction step is 1×10¹⁵ to 5×10¹⁸ ions/cm².
 10. Themethod for producing the GaN substrate according to claim 8, wherein atemperature of the substrate in the phosphorus ion introduction step isfrom 200°-550° C.
 11. The method for producing the GaN substrateaccording to claim 9, wherein a temperature of the substrate in thephosphorus ion introduction step is from 200°-550° C.
 12. The method forproducing the GaN substrate according to claim 8 wherein the phosphorusion introduction step is conducted by ion implantation whereaccelerating energy of the phosphorus ions is 5 to 30 keV.
 13. Themethod for producing the GaN substrate according to claim 9 wherein thephosphorus ion introduction step is conducted by ion implantation whereaccelerating energy of the phosphorus ions is 5 to 30 keV.
 14. Themethod for producing the GaN substrate according to claim 10 wherein thephosphorus ion introduction step is conducted by ion implantation whereaccelerating energy of the phosphorus ions is 5 to 30 keV.
 15. Themethod for producing the GaN substrate according to claim 11 wherein thephosphorus ion introduction step is conducted by ion implantation whereaccelerating energy of the phosphorus ions is 5 to 30 keV.
 16. A methodfor producing a GaN substrate, comprising: a glass layer forming stepfor, before joining an Si base material and an Si thin plateconstituting a surface Si layer, forming on a surface to be a jointsurface thereof, of at least one of the Si base material and the surfaceSi layer, a glass layer having a softening point lower than at least theSiO₂ by a deposition method; a joining step for joining the Si basematerial and the Si thin plate so as to sandwich the glass layertherebetween to form an embedded type substrate in which the Si basematerial layer, the surface Si layer and the embedded glass layer arelaminated; and an SiC forming step for heating the embedded typesubstrate in an atmosphere of hydrocarbon-based gas to convert thesurface Si layer into SiC, and thereafter, cooling the resultingsubstrate to form a single crystal SiC layer on a surface thereof,wherein the SiC forming step further comprises causing the embeddedglass layer between the SiC layer and the Si base material layer to betransformed to cause slippage between the Si base material layer and theSiC layer, to accommodate a difference in shrinkage ratios between theSiC layer and the Si base material layer during performance of themethod, heating and cooling to epitaxially grow the GaN layer on thesingle crystal SiC layer, and thereby causing the embedded glass layerbetween the SiC layer and the Si base material layer to be transformedto cause slippage between the Si base material layer and the SiC layer,to suppress warp of the entire single crystal SiC substrate.